(1) Field of the Invention
The present invention relates to a plastic molding apparatus for packaging a semiconductor device.
(2) Description of the Prior Art
A conventional plastic molding apparatus for molding a semiconductor device is exemplified in FIG. 1.
Referring to FIG. 1, reference numeral 1 denotes a lower half. The lower half 1 has a lower heater plate 3b provided with a plurality of through holes 2b. A lower mold 4b is disposed on the upper surface of the heater plate 3b. A plurality of bores 5b which respectively communicate with the through holes 2b are formed in the lower mold 4b. A plurality of openings or mold cavities 6b are formed in the surface of the lower mold 4b so as to respectively correspond to the bores 5b. A lower insulator 8b is disposed through a frame-like lower spacer 7b on the lower surface of the lower heater plate 3b. A lower ejector plate 11b having lower ejector pins 10b respectively corresponding to the through holes 2b is housed in a space 9b defined by the heater plate 3b, the heat insulator 8b and the spacer 7b. The ejector pins 10b are inserted in the through holes 2b and the bores 5b to be vertically movable therein. The upper surface of the ejector plate 11b is coupled to the lower surface of the heater plate 3b via a coil spring (not shown). An upper push rod (not shown) extends downward from an upper heater plate of an upper half (to be described later) and abuts against the upper surface of the lower ejector plate 11b. The upper push rod serves to urge the ejector plate 11b against the biasing force of the coil spring.
Reference numeral 12 denotes an upper half which is vertically movable relative to the lower half 1. An upper heater plate 3a having a plurality of through holes 2a is disposed in the upper half 12 so as to oppose the lower heater plate 3b. An upper mold 4a is supported below the heater plate 3a.
A plurality of bores 5a which respectively communicate with the through holes 2a are formed in the upper mold 4a. A plurality of openings or mold cavities 6a are formed in the surface of the upper mold 4a so as to respectively correspond to the bores 5a. An upper insulator 8a is disposed through a frame-like spacer 7a on the upper surface of the heater plate 3a. An upper ejector plate 11a having upper ejector pins 10a respectively corresponding to the through holes 2a is housed in a space 9a defined by the heater plate 3a, the heat insulator 8a and the spacer 7a. The ejector pins 10a are inserted in the through holes 2a and the bores 5a to be vertically movable therein. The lower surface of the ejector plate 11a is coupled to the upper surface of the heater plate 3a via a coil spring (not shown). A lower push rod (not shown) extends upward from the lower heater plate 3b of the lower half (as described above) and abuts against the lower surface of the upper ejector plate 11a. The lower push rod serves to urge the ejector plate 11a against the biasing force of the coil spring.
Pots, runners and gates (not shown) are disposed between the upper mold 4a and the lower mold 4b to serve to inject a plastic material into the openings 6b and 6a.
The operation of the plastic molding apparatus shown in FIG. 1 will be described.
A lead frame 13 with semiconductor elements mounted thereon is set in cavities of the lower mold 4b of the lower half 1.
When the upper half 12 is moved downward, the upper push rod urges and moves the lower ejector plate 11b downard against the biasing force of the coil spring for coupling the lower heater plate 3a and the lower ejector plate 11b. The lower ejector pins 10b are also moved downward. At the same time, the lower push rod urges and moves the upper ejector plate 11a upward against the biasing force of the coil spring for coupling the upper heater plate 3a and the upper ejector plate 11a, so that the upper ejector pins 10a are also moved upward. As a result, mold clamping is performed.
A plastic material is injected into the cavities through the pots, runners and gates to seal the semiconductor elements (not shown) of the lead frame 13 by plastic layers 14.
Thereafter, the upper half 12 is separated from the lower half 1, the urging force acting on the lower ejector plate 11b is released, and the lower ejector plate 11b is moved upward by the biasing force of the coil spring coupled between the lower heater plate 3b and the lower ejector plate 11b. The lower ejector pins 10b inserted in the through holes 2b and the bores 5b extend upward from the bottom surfaces of the openings 6b of the lower mold 4b. At the same time, the urging force acting on the upper ejector plate 11a by means of the lower push rod is released, and the upper ejector plate 11a is moved downward by the biasing force of the coil spring coupled between the upper heater plate 3a and the upper ejector plate 11a. The upper ejector pins 10a inserted in the through holes 2a and the bores 5a extend downward from the bottom surfaces of the openings 6a of the upper mold 4a. As a result, the lead frame 13 is released from the upper and lower halves 12 and 1.
However, in the plastic molding apparatus molding apparatus described above, the through holes 2b and 2a of the lower and upper heater plates 3b and 3a respectively communicate with the bores 5b and 5a of the lower and upper molds 4b and 4a. The lower and upper ejector pins 10b and 10a mounted on the lower and upper ejector plates 11b and 11a are vertically movable in the through holes 2b and 2a and the bores 5b and 5a, respectively. Therefore, when the outer dimensions of the products and pitches of products in the lead frame 13 change in accordance with different types of products, the shapes of the lower and upper molds 4b and 4a must be changed, and the pitches of the ejector pins 10b and 10a must also be changed. Every time the type of product changes, the lower mold 4b, the upper mold 4a, the heater plates 3b and 3a, the spacers 7b and 7a, and the heat insulators 8b and 8a must be replaced with proper ones. The manufacturing and material costs are increased.
Furthermore, the heater plates 3b and 3a and the spacers 7b and 7a are greater than the lower and upper molds 4b and 4a in size and weight. The replacement operation is time-consuming and cumbersome, and replacement cannot be immediately performed until the apparatus is cooled, since the molding apparatus is heated at a molding temperature, thus resulting in heat loss and low replacement efficiency. As a result, the utilization efficiency of the apparatus using such molds is degraded.